Aqueous extract of Swietenia macrophylla leaf exerts an anti-inflammatory effect in a murine model of Parkinson’s disease induced by 6-OHDA

IntroductionParkinson’s disease affects 2% of the population aged over 65 years and is the second most common neurodegenerative disorder in the general population. The appearance of motor symptoms is associated with the degeneration of dopaminergic neurons in the nigrostriatal pathway. Clinically significant nonmotor symptoms are also important for severe disability with disease progression. Pharmacological treatment with levodopa, which involves dopamine restitution, results in a temporary improvement in motor symptoms. Among the mechanisms underlying the pathogenesis of the disease are exacerbated oxidative stress, mitochondrial dysfunction, and neuroinflammation. A phytochemical prospecting study showed that the aqueous extract of the leaves from Swietenia macrophylla (Melineaceae), known as mahogany, has polyphenols with antioxidant and anti-inflammatory capacity in a significantly higher percentage than leaf extracts from other Amazonian plants. Furthermore, the antioxidant and anti-inflammatory capacity of aqueous extract of mahogany leaf has already been demonstrated in an in vitro model. In this study, we hypothesized that the aqueous extract of mahogany leaf (AEML) has a neuroprotective effect in a murine model of Parkinson’s disease induced by 6-hydroxidopamine (6-OHDA), due to antioxidant and anti-inflammatory properties of its phenolic compounds.MethodsMice were treated daily with the mahogany extract at a dose of 50 mg/kg, starting 7 days before 6-OHDA infusion until post-surgery day 7.Results and discussionThe animals from the 6-OHDA/mahogany group, which corresponds to animals injected with the toxin and treated with aqueous extract of the mahogany leaf, presented distinct behavioral phenotypes after apomorphine challenge and were therefore subdivided into 2 groups, 6-OHDA/mahogany F1 and 6-OHDA/mahogany F2. The F1 group showed a significant increase in contralateral rotations, whereas the F2 group did not show rotations after the apomorphine stimulus. In the F1 group, there was an increase, although not significant, in motor performance in the open field and elevated plus maze tests, whereas in the F2 group, there was significant improvement, which may be related to the lesser degree of injury to the nigrostriatal dopaminergic pathway. The TH+ histopathological analysis, a dopaminergic neuron marker, confirmed that the lesion to the nigrostriatal dopaminergic pathway was more pronounced in 6-OHDA/mahogany F1 than in 6-OHDA/mahogany F2. Our main result consisted of signs of improvement in the inflammatory profile in both the F1 and F2 6-OHDA/mahogany groups, such as a lower number of IBA-1+ microglial cells in the ventral striatum and substantia nigra pars compacta and a reduction in GFAP+ expression, an astrocyte marker, in the dorsal striatum. In this study, several bioactive compounds in the aqueous extract of mahogany leaf may have contributed to the observed beneficial effects. Further studies are necessary to better characterize their applicability for treating chronic degenerative diseases with inflammatory and oxidative bases, such as Parkinson’s disease

Modelo de doença de parkinson em camundongos baseado na injeção unilateral 6-hidroxidopamina no estriado: caracterização do curso temporal das alterações comportamentais e da degeneração nigroestriatal

Parkinson‘s disease (PD) is a common neurodegenerative disease that affects mainly elderly people. It is characterized by the progressive cell death of dopaminergic neurons in the nigrostriatal system, which causes the development of the classic tetrad of symptoms: resting tremor, muscular rigidity, bradikynesia and postural instability. There is evidence that both genetic and environmental factors play a role in the development of the disease. In order to better understand the mechanisms undelying this disease, several animal models have been used to mimic some aspect of the dopaminergic degeneration. The intracerebral injection of 6-OHDA has been one of the most used PD model. This toxin is preferentially injected into the striatum or in the substantia nigra to provoke a selective degeneration of dopaminergic neurons from the nigrostriatal pathway. When a unilateral injection is used, the animals display a stereotypical rotational behavior after pharmacological induction, and such behavior has been largely used as a measure of the degree of nigroestriatal degeneration. This model is well characterized in rats and has been an useful tool to test neuroprotective therapies. Mice, as much as rats, are also largely used in studies of DP, but the 6-OHDA model has not been well described. The objective of the present work was to improve the characterization of the hemiparkinsonism model based on a single unilateral intraestriatal injection of 6-OHDA in C57BL6 mice, to provide a more detailed evaluation of the temporal course of the neuronal dopaminergic degeneration in the substantia nigra and to establish the degree of correlation between the degeneration and behavioral changes. Our results showed that a single injection of 10 μg of 6-OHDA into the striatum causes progressive degeneration of nigral dopaminergic neurons dependent of survival time, and that there is a high correlation between the rate of degeneration and the rotational behavior induced by apomorphine. Spontaneous motor behaviors such as ambulation and rearing had a lower correlation with the degeneration. Therefore, we suggest that the rotational behavior induced by apomorphine provides a good measure of the degree of asymmetry in the nigrostriatal pathway of mice with 6- OHDA-induced hemiparkinsonism and that it can indeed be an useful tool in experiments to test therapies with neuroprotective potential for Parkinson’s disease.A Doença de Parkinson (DP) é uma doença neurodegenerativa comum, que afeta principalmente pessoas idosas. Caracteriza-se pela morte progressiva de neurônios dopaminérgicos do sistema nigroestriatal, levando ao aparecimento de sintomas que caracterizam a tétrade clássica da doença: tremor em repouso, rigidez muscular, bradicinesia e instabilidade postural. Há evidências de que tanto fatores genéticos como ambientais contribuam para o desenvolvimento da doença. A fim de se melhor entender os mecanismos subjacentes à doença vários modelos animais foram desenvolvidos que mimetizam algum aspecto da degeneração dopaminérgica envolvida na DP. A injeção intracerebral de 6-OHDA é um dos modelos mais utilizados. Esta toxina é preferencialmente injetada no estriado ou na substância negra, onde promove destruição seletiva de neurônios catecolaminérgicos da via nigroestriatal. Quando a injeção é unilateral, os animais apresentam um comportamento rotatório estereotipado após indução farmacológica e tal comportamento tem sido muito usado pra medir o grau de degeneração nigroestriatal. Este modelo está bem caracterizado em ratos e tem sido uma ferramenta útil para testar terapias celulares ou farmacológicas com potencial neuroprotetor. Camundongos, assim como ratos, também são largamente utilizados em diversos estudos relacionados à DP. O presente trabalho teve como objetivo melhorar a caracterização do modelo de hemiparkinsonismo baseado em uma injeção única intraestriatal unilateral de 6- OHDA em camundongos C57BL6, visando avaliar o curso temporal da degeneração dos neurônios dopaminérgicos na substância negra e o grau de correlação entre a degeneração neuronal e alterações comportamentais. Os nossos resultados mostraram que, após uma única injeção de 10 μg de 6-OHDA no estriado, ocorre degeneração progressiva dos neurônios nigrais em função do tempo de sobrevida, e que existe uma correlação alta entre a taxa de degeneração e o comportamento rotatório induzido por apomorfina. Comportamentos motores espontâneos de ambulação e bipedestação tiveram correlação menor com a degeneração. Portanto, sugerimos que o comportamento rotatório induzido por apomorfina é um bom indicativo do grau de assimetria na via nigroestriatal de camundongos com hemiparkinsonismo induzidos por 6-OHDA e que pode ser uma ferramenta muito útil em experimentos que visem testar terapias com potencial neuroprotetor para a doença de Parkinson